This invention relates to plastic films and sheet materials containing poly(paramethyl styrene), herein referred to as PPMS. In particular, it concerns oriented films of PPMS and methods for manufacturing films, foils, sheets, laminates or similar products.
It is well known in the plastics arts that styrene homopolymers and copolymers are useful in making low cost films and sheet products. Alkyl-substituted styrenes are well known as monomers for addition polymerization, especially .alpha.-methyl styrene and various mixed isomers of ring-substituted methyl styrene. These mixed isomers are usually a reaction product of ethylated toluene which has been dehydrogenated to obtain a mixture rich in para and ortho isomers. Biaxially oriented polystyrene is generally known and described in U.S. Pat. No. 2,997,743 (Isaksen et al.), U.S. Pat. No. 3,619,445 (Carlson), and U.S. Pat. No. 4,011,357 (Haase).
Various copolymers of acrylonitrile containing a minor amount of styrene or other comonomers, such as 4-methylstyrene, are disclosed in U.S. Pat. No. 4,039,734 (Hendy) as being suitable for making biaxially-oriented films. Also, the uncharacterized vinyl toluene monomers, usually a mixture of isomers, with large amounts of ortho and meta compounds, are known as copolymeric materials, of instance as hot drawn film disclosed in U.S. Pat. No. 3,322,855 (Fukushima et al.).
Molecular orientation of thermoplastic resins can be achieved by stretching a sheet, usually 2 to 8 times its original linear dimension. This stretching operation can be performed uniaxially or biaxially by several techniques, for example by sequentially stretching a continuous strip in the machine and transverse directions, as taught in U.S. Pat. No. 2,695,420 (Longstreth et al.).